Distrvacuum or not?

[flyinlow]

Thirty years ago I tried running manifold vacuum to the advance unit. It made my eyes burn more when I stood behind an idling 440 car. I had access to a Sun exhuast annilizer. Unburnt Hydrocarbon levels went up at idle with manifold vacuum advance. Not sure why. The engine idled faster ,and after I slowed the idle speed back down, it seamed rougher. Some cars came that way in the sixtys (GM). I went back to ported vacuum advance.

[A383Wing]

I tried the same thing years ago...ran like crap....

[tan top]

Thirty years ago I tried running manifold vacuum to the advance unit. It made my eyes burn more when I stood behind an idling 440 car. I had access to a Sun exhuast annilizer. Unburnt Hydrocarbon levels went up at idle with manifold vacuum advance. Not sure why. The engine idled faster ,and after I slowed the idle speed back down, it seamed rougher. Some cars came that way in the sixtys (GM). I went back to ported vacuum advance.

I tried the same thing years ago...ran like crap....

yeah  think i made a mistake  , when i tried vacuum advance on my thunder  ,  went buy the instructions  see other thread ,  & used manifold port , should of copied the carter OEM & used the timed (above throttle plate)   (will get round to sorting it sometime  ) but runs  strong  with mechanical advance only  
had the original carter & points distributor vacuum dialed in real good as well

[mhinders]

Last summer I spent a lot of time tinkering with the vacuum advance...I really wanted to use it for my street car. However, I have a low vacuum engine (7-10 in) and it was simply impossible to get it to run around idle with the vacuum advance connected. For example, putting the auto into gear, the revs drop, the vacuum drops, the ignition advance drops, the revs drop even further...the engine stalls.
I agree, keep it blocked if you have a low vacuum engine.
Martin

[b5blue]

Ported vacuum advance needs a dizzy set for ported. I don't know how FBO figures it out but it works well. 

[tatrick2me]

Hey Ron:

Not to Challange your vast knowlage but there was a rightup in Feb 2010 Mopar Action ( Jay Leno {Turbine}) in which Rich Ehrenberg Stated....

"OK yours truly has never been known for subtlety.And this cant be candy-coated. So I'll just say it:Anyone who drives on the street and doesn't run
Vacuum advance is an idiot."

I 2nd this, without the advance working timing would be st at 36 degrees all the time. When starting the engine would kick so hard it would break the starter.



As opposed to me simply posting Quotes from Rich
I'll find a link to the story or at least Scan and Copy it, It was well written Story.


Ron

[firefighter3931]

I 2nd this, without the advance working timing would be st at 36 degrees all the time. When starting the engine would kick so hard it would break the starter.

That statement is incorrect. You're confusing mechanical with vacuum advance. 

The only way to get full advance at idle is to lock out the distributor. Fwiw, my old 446 had it's distributor locked out and started/idled fine @ 35* advance. Every engine combination is different and once you add some cam/compression/big exhaust the ballgame changes. 


Ron

[flyinlow]

Last summer I spent a lot of time tinkering with the vacuum advance...I really wanted to use it for my street car. However, I have a low vacuum engine (7-10 in) and it was simply impossible to get it to run around idle with the vacuum advance connected. For example, putting the auto into gear, the revs drop, the vacuum drops, the ignition advance drops, the revs drop even further...the engine stalls.
I agree, keep it blocked if you have a low vacuum engine.
Martin

Yea , if you are losing the vacuum advance and possibly some centrifugal when you put the car in drive this will make it very hard to have a consistent idle.
Finding the right springs to have little or no centrifugal advance below 1000 rpm (engine) and be all advance by say 2500- 3000 rpm can take several tries.
Some Mopar vacuum advance units are hex wrench adjustable to allow vacuum as low as 10" to activate them.